Surface-enabled superior lithium storage of high-quality ultrathin NiO nanosheets

Two-dimensional nanomaterials hold great potential for next-generation energy storage and conversion devices. Here, we report a large-scale synthesis of high-quality ultrathin NiO nanosheets. The well-defined nanosheets show a graphene-like morphology with large planar area, ultrathin thickness (<2 nm), and high percentage of surface atoms. In comparison with the bulk material, the NiO nanosheets exhibit unique surface and electronic structure with considerable under-coordinated surface nickel atoms and crystal lattice volume expansion. The detected local coordination geometry and the electronic states endow the ultrathin NiO nanosheets with great potential in surface-dependent electrochemical reactions and catalytic processes. When used as anode materials for lithium-ion batteries, the ultrathin NiO nanosheets exhibit a high reversible lithium storage capacity of 715.2 mA h g(-1) at 200 mA g(-1) current density in 130 cycles with an excellent cycling stability and rate capability. In particular, the large-area ultrathin 2D nanostructure can shorten lithium ion diffusion paths and provide a large exposed surface for more lithium-insertion channels. The large-scale and cost-efficient synthesis and the excellent electrochemical performance highlight the high-quality ultrathin 2D NiO nanosheets as a competitive anode material for lithium-ion batteries.